Comparison of Split or Single Application of Gypsum for Wild Lowbush Blueberry (Vaccinium angustifolium Ait.)

Gypsum (CaSO4 center dot 2H(2)O) was evaluated as a single pre-emergent application (4,482 kg/ha) or a split application (2,242 kg/ha pre-emergent and 2,242 kg/ha 2 weeks later) for its effect on soil nutrient release, nutrient uptake, and plant growth at two commercial lowbush blueberry fields (Clary Hill and Marshville, Maine). Gypsum applications were compared to diammonium phosphate (448 kg/ha) and a control using 0.9 m x 15 m plots arranged in a randomized complete block design with six blocks. Composite leaf and soil samples were collected within each treatment plot in July 2009 and analyzed for nutrient concentrations. Within each treatment plot, stems from four randomly placed 0.023 m(2) quadrats were collected in October 2009 for stem length, branching, and flower bud measurements. Gypsum raised soil Ca and S concentrations at both fields compared to diammonium phosphate and the control. One of the fields (Marshville) was deficient in leaf N and P. Diammonium phosphate raised leaf N and P concentrations compared to the controls at both fields; but gypsum (single or split application) raised leaf N and P only at the deficient Marshville field. Diammonium phosphate increased stem branching, number of branches, length of branched stems, and average stem length at both fields. Gypsum treatments did not affect stem characteristics at either field except for stem branching, which was raised by the split application at the deficient Marshville field. Blueberry yield was increased by diammonium phosphate at Clary Hill and Marshville by 57 and 117%, respectively, compared to the control. Neither of the gypsum treatments increased yield. A split application of gypsum was not more effective than a single application.